Martinson watched the developments out of Boston very closely and with concern.

“One person who finished pretty close and said he did see the explosion … was definitely very shaken up,” said Martinson.

He was relieved to learn everyone he knows is safe.

Ryan Callahan, also with Philadelphia Runner was in awe.

“We were actually supposed to be going up there, I mean we pulled out the day before,” said Callahan.

They say the “unknowns” like who is behind this and why this happened have many in the close-knit running community on edge.

“It’s probably the most elite marathon,” said Callahan.

Those who made it into the Boston Marathon are considered “the best of the best” from around the world.

“People are reaching their goals, people are accomplishing this major thing off their bucket list and it’s a very festive environment,” said Callahan, adding, “It’s tragic, but it’s then also more so tragic that it comes on this really exciting event.”